[Users] Disk statistics

Hi All, Because of an question on IRC I looked at /api/disks/long-disk-id/statistics but all values (datum) are ZERO. Its a disk of a VM that was running a dd if=/dev/vda of=/dev/null so I would expect something to show up (Did various webpage refreshes of the mentioned stats url). I also have ovirt-guest-agent running on that VM, in case it matters and the disk is on a NFS data domain. What am I missing? Regards, Joop